At least five, and possibly as many as 25, children in California have polio-like symptoms, including paralysis of limbs and breathing problems.

Tests show that the children do not have polio and that many have been vaccinated against it. Since the first case was reported in 2012, two patients have been diagnosed with enterovirus-68. The rare virus, which has been linked to severe breathing problems, is from the same family as poliovirus. The causes of the other cases have not been identified, and it is not clear if they are linked.

Scientists say the cases do not appear to represent an epidemic, although similar symptoms have also been reported in children in Asia and Australia. More information will be presented at the annual meeting of the American Academy of Neurology in April.